Showing papers by "Allan J. Baker published in 1993"
TL;DR: It is shown that population fragmentation in Pleistocene refuges is the most plausible mechanism of mtDNA differentiation but at a much earlier time scale than suggested previously with morphometric data.
Abstract: Hypervariable segments of the control region of mtDNA as well as part of the cytochrome b gene of Dunlins were amplified with PCR and sequenced directly. The 910 base pairs (bp) obtained for each of 73 individuals complete another of the few sequencing studies that examine the global range of a vertebrate species. A total of 35 types of mtDNA were detected, 33 of which were defined by the hypervariable-control-region segments. Thirty of the latter were specific to populations of different geographic origin in the circumpolar breeding range of the species. The remaining three types indicate dispersal between populations in southern Norway and Siberia, but female-mediated flow of mtDNA apparently is too low to overcome the effects of high mutation rates of the control-region sequences, as well as population subdivision associated with historical range disjunctions. A genealogical tree relating the types grouped them into five populations: Alaska, West Coast of North America, Gulf of Mexico, western Europe, and the Taymyr Peninsula. The Dunlin is thus highly structured geographically, with measures of mutational divergence approaching 1.0 for fixation of alternative types in different populations. High diversity of types within populations as well as moderate long-term effective population sizes argue against severe population bottlenecks in promoting this differentiation. Instead, population fragmentation in Pleistocene refuges is the most plausible mechanism of mtDNA differentiation but at a much earlier time scale than suggested previously with morphometric data.
196 citations
TL;DR: This article investigated cultural evolution in populations of common chaffinches (Fringilla coelebs) in the Atlantic islands (Azores, Madeira, Canaries) and neighboring continental regions (Morocco, Iberia) by employing a population memetics approach.
Abstract: We investigated cultural evolution in populations of common chaffinches (Fringilla coelebs) in the Atlantic islands (Azores, Madeira, Canaries) and neighboring continental regions (Morocco, Iberia) by employing a population memetics approach. To quantify variability within populations, we used the concept of a song meme, defined as a single syllable or a series of linked syllables capable of being transmitted. The frequency distribution of memes within populations generally fit a neutral model in which there is an equilibrium between mutation, migration, and drift, which suggests that memes are functionally equivalent. The diversity of memes of single syllables is significantly greater in the Azores compared to all other regions, consistent with higher population densities of chaffinches there. On the other hand, memes of two to five syllables have greater diversity in Atlantic island and Moroccan populations compared to their Iberian counterparts. This higher diversity emanates from a looser syntax and increased recombination in songs, presumably because of relaxed selection for distinctive songs in these peripheral and depauperate avifaunas. We urge comparative population memetic studies of other species of songbirds and predict that they will lead to a formulation of a general theory for the cultural evolution of bird song analogous to population genetics theory for biological traits.
109 citations
TL;DR: The Rufous-collared Sparrow, Zonotrichia capensis, is widely distributed in neotropical America and shows extensive variation in its learned song, but the mtDNA variability is interpreted as a reflection of secondary introgression between two well-differentiated subspecies whose ranges abut in this region.
Abstract: The Rufous-collared Sparrow, Zonotrichia capensis, is widely distributed in neotropical America and shows extensive variation in its learned song. In northwestern Argentina it exhibits song dialects which map closely onto the distribution of natural vegetation assemblages. To date, there is no evidence ofa correlation between genetic (allozyme) variation and dialects. However, recent genetic structuring produced through philopatry and assortative mating by dialect is difficult to demonstrate statistically with such proteinencoding nuclear genes. Therefore, we assayed variation in more rapidly evolving mitochondrial DNA along a 50 km transect, which spans three dialect boundaries between four adjacent habitat-types (from ~ 1,800 m to ~-3,000 m), using restriction fragment length polymorphism analysis. This revealed exceptional diversity (41 clones from 42 individuals), a level comparable with DNA-fingerprinting, and higher than reported in any passerine over such a small area to date. The degree of nucleotide divergence between the two main clusters of mtDNA haplotypes implies a separation time in excess of one million years. The mtDNA variability is not related to song dialects; rather it is interpreted as a reflection of secondary introgression between two well-differentiated subspecies whose ranges abut in this region.
31 citations
TL;DR: It was found that deeper bodied fish from one population of northern redbelly dace were significantly more adept at capturing evasive prey than were relatively shallow-bodied fish from another population.
Abstract: Geographic differences in body shape among 18 populations of northern redbelly dace in three regions of Ontario (Sudbury, Algonquin Provincial Park, and Kingston) were quantified with truss analysis. Principal component analysis of size-adjusted residuals of the trusses revealed that 35.11% of the morphological variation in body shape is explained on principal component I. This axis describes the major trend in body shape variation, ranging from populations in which fish are relatively deep-bodied to those in which fish are more shallow-bodied. Shape variation among populations in Algonquin Park spanned the range observed among all three regions in Ontario. Experiments were thus conducted on two Algonquin populations differing considerably in body shape, and it was found that deeper bodied fish from one population were significantly more adept at capturing evasive prey than were relatively shallow-bodied fish from another population. This finding is not only consistent with functional analysis of fish sha...
15 citations
TL;DR: The genetic similarity of the masked and prairie shrews implies that S. cinereus is a paraphyletic taxon and suggests a recent divergence of these taxa, perhaps in the late Pleistocene or the early Holocene.
Abstract: Populations of the masked shrew ( Sorex cinereus ) and the prairie shrew ( S. haydeni ) occurring in sympatry in Alberta were compared genetically with each other and with populations of S. cinereus across Canada using protein electrophoresis of 33 loci. Despite distinct morphologic differences between S. cinereus and S. haydeni , in Alberta these taxa were less genetically differentiated (Ne's genetic distance, D N = 0.006; Rogers' genetic distance, D R = 0.047) than were conspecific populations of S. cinereus across Canada ( D N = 0.019; D R = 0.058). Although there were no fixed allele differences among the populations sampled, there was a unique allele at a moderate frequency in S. haydeni (PEP-SB, 0.375). This may be indicative of no gene flow between these two taxa and thus they may be valid species. The genetic similarity of the masked and prairie shrews implies that S. cinereus is a paraphyletic taxon and suggests a recent divergence of these taxa, perhaps in the late Pleistocene or the early Holocene. Among populations of S. cinereus across Canada, the pattern of differentiation is consistent with a biogeographic model in which shrews re-colonized Canada from multiple refugia following the retreat of the Wisconsin glaciers.
14 citations
TL;DR: Examination of chromosomal and mitochondrial DNA variation in four laboratory colonies revealed two ancient, divergent genotypic assemblages, corresponding to geographic distributions of sex chromosomes, and sex chromosome morphology is geographically structured and correlated with proposed southern and northern refugia.
Abstract: Genetic differentiation among populations and speciation in Dicrostonyx is hypothesized to have resulted from either allopatric divergence in glacial refugia during the Wisconsin or sympatric processes uncorrelated with refugial isolation. We examined chromosomal and mitochondrial DNA variation in four laboratory colonies, representing three species, in a preliminary evaluation of these hypotheses. Chromosomal variation is extensive among populations, diploid numbers ranging from 38 to 50. Autosomal variation appears to be due primarily to Robertsonian rearrangements and additions of supernumerary chromosomes, and is geographically unpatterned. Sex chromosome morphology is geographically structured and correlated with proposed southern and northern refugia. Restriction fragment analysis of mitochondrial DNA revealed two ancient, divergent genotypic assemblages, corresponding to geographic distributions of sex chromosomes. Autosomal variation, and any resulting reproductive isolation, probably is recent an...
14 citations